1. Field of the Invention
The present invention relates to a chamber free gas purge method and apparatus for establishing an inert atmosphere zone at the root side of a weld seam. In another aspect, the invention relates to the concept of strategically providing an inert atmosphere to the root side of a weld .joint through a porous medium whereby the jet-like thrust of a plasma arc draws the continuously supplied inert atmosphere into the path of the molten or high temperature solid weld zone. In yet another aspect, the invention relates to a chamber free provision of an inert atmosphere on the root side of a fusion welding which permits open view of the welding seam.
2. Description of Related Art
Fusion welding of oxygen reactive materials such as aluminum-lithium alloys, titanium and the like, requires that the molten weld zone and the local solid areas at high temperatures be shielded from the normal atmosphere or oxygen to prevent degradation of the welded area so as to avoid producing weld discontinuities and other potential defects. Full penetration welding of these reactive materials with a plasma arc welding process, in the "keyhole mode", requires that the root side of the joint be shielded with relative precision due to the additional implications brought on by the plasma arc thrusting to the root side of the weld seam. Most current root side welding methods involve encasing a section of or the entire length of the root side weld seam in a chamber which is purged with inert gas until the atmosphere contained within is relatively free of oxygen. These chambers may be fixed to the weld tooling or may be mobile and travel synchronously with the welding arc.
As the need for lighter and/or stronger materials has increased, particularly with regard to aerospace constructions, the interest in and the use of titanium and its alloys, likewise, has been increased. Although titanium and titanium alloy work pieces have the desired and needed characteristics of exceptional tensile strength and heat resistance, said work pieces are susceptible to atmospheric contamination during welding. Accordingly, in joining said work pieces by welding, it is generally necessary to weld the work pieces in a rigid chamber which has been purged of ambient air through use of inert gas. Use of the chamber requires enormous waste of time and waste of the purging inert gas used.
The above-described root side purging chamber utilization has further undesired aspects. The atmosphere contained within the chamber must be monitored for pressure and for oxygen content. The chambers, depending upon the configuration, will restrict viewing of the root side of the welding operation partially or fully, unless a fully transparent chamber is utilized. Viewing the root side of the plasma arc weld during full penetration is generally considered to be the best method of monitoring arc to seam alignment and penetration characteristics. The inert gas consumption requirement of these chambers is relatively large due to requirements of maintaining a low oxygen level.
Several approaches have been utilized to modify the burden of the welding chamber such as by an inflatable, inert gas purged welding chamber assembly. The welding chamber of the assembly is defined by a collapsible, reusable inflatable member. In another approach, a purge gas unit establishes an enclosed zone for purge gas within tubes or pipes having portions which are to be joined by welding. The purge gas unit includes a first bladder positioned on one side of the welding location and a second bladder positioned on the other side of the location.
It is, therefore, readily apparent that what is needed in the art, and is not currently available, is an apparatus and method which eliminate the aforementioned disadvantages and which also permit the uncontaminated welding of titanium, titanium alloys, aluminum-lithium alloys and the like, and other work pieces of other metals and metal alloys which are reactive base materials in the presence of oxygen.